Conventional breathing assistance systems typically include a gas delivery system, a patient interface to deliver gas to one or more breathing passages of the patient, and a connection system between the gas delivery system and the patient interface. Such breathing assistance systems may be used, e.g., for mechanical ventilation of a patient's lungs and/or treatment of an apnea or other medical condition. The gas delivery system may include a controller configured to vary the flow rate, pressure, and/or other characteristics of the gas delivered to the patient, based on the intended treatment or condition of the patient.
Many modern ventilators include sensors operable to measure various parameters regarding the patient's breathing patterns and/or the operation of the ventilator, and may allow the caregiver to adjust ventilator settings to select or adjust the ventilation strategy being implemented. For example, a gas delivery system may sense one or more of the following parameters: airway pressure, exhaled volume, ventilation mode, type of breath, mean airway pressure, peak airway pressure, PEEP/CPAP pressure, plateau pressure, respiratory rate, I:E ratio, tidal volume, minute volume, and spontaneous minute volume.
Clinical treatment of a ventilated patient often requires that physiological characteristics of the patient be monitored to detect the effects of a particular ventilation strategy on a patient or changes in the patient's breathing patterns. Saturation of Peripheral Oxygen (SpO2) is an estimation of the oxygen saturation level in a patient's blood usually measured with a pulse oximeter and is one physiological characteristic that may be used in ventilation control. For example, a gas delivery system may control the fraction of inspired oxygen (FiO2) in the gas delivered based on the SpO2 measured. One embodiment employing this example includes a controller that may adjust the FiO2 by an amount proportional to the difference between a measured SpO2 and a user-specified target SpO2.